The embodiments described herein relate generally to vacuum relief valves and, more particularly, to vacuum relief valves for use with railcars.
Known vacuum relief valves are coupled to containers, such as a tank or tanker car (i.e., a truck tanker car or a railcar tanker car), for relieving a vacuum formed within the container. The vacuum is typically caused by pressure and/or temperature changes that occur within the container. When a vacuum forms in the container, the vacuum (i.e., the pressure difference) exerts a force on a stem of the relief valve that causes the stem to move and the valve to open. Air from outside the container is then allowed to enter the container through the valve to relieve the vacuum (i.e., to equalize the pressure difference between the inside of the container and the outside of the container).
At least some known vacuum relief valves are “step” type vacuum relief valves that enable an operator to push downward on a top of the valve to relieve a vacuum within a container. However, at least some known step type vacuum relief valves can be accidentally depressed, which may allow materials other than air to enter and/or exit the container through the valve. Further, at least some known step type vacuum relief valves include a seat located generally midway between a top and a bottom of the valve.
At least some other known vacuum relief valves are “no-step” type vacuum relief valves that cannot be manually operated while coupled to a container. Some known no-step vacuum relief valves include a flanged connection and a seat that is positioned generally midway between a top and a bottom of the valve. Further, such known vacuum relief valves vent air through a top of a body of the valve.
In both types of known vacuum relief valves, the seat and/or a seal positioned on the seat is accessed by disassembling the valve because of the midway location of the seat. Such known vacuum relief valves are serviced, inspected, and/or repaired, by removing the valve from the container and disassembling the valve. When these types of known vacuum relief valves are disassembled while still coupled to the container, it is possible that the stem can become uncoupled from the valve and fall into the container causing the material stored within the container to be contaminated.
Accordingly, it is desirable to provide a vacuum relief valve that can be inspected, including inspecting the valve seat and seal area, without removing the valve from the container. Such inspections allow users to confirm that the valve is seating properly and that no material has accidentally leaked from the container. It is also desirable to provide a vacuum relief valve that can be serviced, including replacing seals in the valve seat area, without having to disassemble the valve. By avoiding valve disassembly, the risk of uncoupling the valve stem so that it falls into the container can be reduced. Further, it is desirable to provide a vacuum relief valve that has tamper resistant and/or tamper evident features to insure that contents of the container have not been contaminated and/or accidentally released.